Journal of International Council on Electrical Engineering Vol. 3, No. 4, pp.323~329, 2013 http://dx.doi.org/10.5370/JICEE.2013.3.4.323
Simple Measurement System for Indoor Power flow Distributions using Voltmeters at Electrical Outlet Yuhei Nozaki†, Yasunori Mitani*, Qudaih Yaser* and Masayuki Watanabe* Abstract – In order to monitor and manage the electric power consumption and distribution in a building or a house dispersedly implemented digital power meters are utilized, while the meters are very costly due to the complicated numerical operation or due to the multi-functionality such as measurements of reactive power, power factor, integrating power and so on. Therefore a simple combination of current transformer (CT) and potential transformer (PT) with post processing of collected data is used for energy usage diagnosis process. However, as long as the power lines are usually behind the walls the CT installation is not easy. In this paper a set of voltmeters dispersedly installed at power outlets is proposed as a monitoring system for power distribution to each outlet. Experimental results show the advantage of the proposed scheme in the sense that it does not disturb the usage of electric appliances and that the system configuration is simple. The proposed system was applied to the monitoring system for avoiding overload conditions or power losses. Keywords: Voltmeter, Power consumption, Outlet, Voltage measurement, Power estimation
society [3][4] . It is essential to understand the power usage of each consumer through a smart meter in order to achieve optimization of power system operation with a smart grid. In addition the interface between the smart meter and the Home Energy Management System (HEMS) should be the key issue to realize smarter energy optimization. The digital power meter for this purpose, however, is expensive since it holds digital multi-functions to deal with various parameters such as current, voltage, frequency power factor and so on. In addition, clamping the power line is general method for measuring the current. Therefore, when the power consumption of each outlet in a room is measured, implementation of power meter is not easy because installing electrical equipment, which has the ability to measure current between the electrical outlet and the instrument or the current requires clamping the power line which is hidden behind the wall [5]. In this paper, therefore, a set of voltmeters dispersedly installed at power outlets is proposed as a monitoring system for power distribution to each outlet. As a result, indoor power consumption was estimated with inexpensive and easy way by applying the proposed estimation method.
1. Introduction Recently people are deeply aware of the climate changes associated with the abnormal weather and rise of sea due to the green house effects mainly caused by massive amount of CO2 emission. Since the industrial revolution a large amount of fossil fuels such as petroleum and coal have been used as driving resources for the steam engines and turbines and combustion engines where huge amount of CO2 has been released from them [1][2]. In addition the east Japan large earthquake on March 11, 2011 changed the conscious of Japanese against energy usages, especially on the electric power. As a result of shortage of electric power supply in summer and winter, which correspond to the sharp peak season of energy demand in Japan, everyone is more conscious about energy. Thus every energy consumer needs to understand the electric power usage in the house or the office, thereby to address energy conservation measures consciously by visualizing the electric power flows becomes important. In this circumstance the application of smart grid technology has been investigated for the purpose of constructing the area power network to realize a low-carbon
2. Simple Measurement System of Indoor Power Flow Distribution by Multi-point Simultaneous Voltage Measurements
†
Corresponding Author: Dept. of Electrical and Electronic Engineering, Kyushu Institute of Technology, Japan (
[email protected]) * Dept. of Electrical and Electronic Engineering, Kyushu Institute of Technology, Japan (
[email protected]) Received: September 20, 2013; Accepted: September 30, 2013
2.1 The basic principle to estimate active power
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Simple Measurement System for Indoor Power flow Distributions using Voltmeters at Electrical Outlet
percentage of voltage drop by resistance of line between two measurement points when the load is connected to the outlet. And, Vs is the reference voltage when the reference load is connected. P can be estimated from only information of voltage difference by using this data when any kinds of load are connected. In addition, a voltmeter can be installed in parallel with a connected appliance, which means that the appliance needs not be disconnected out of the outlet because this estimation method for active power uses only voltage information. Therefore, this technique can measure the active power without measuring the current. [5]
Fig. 1. Diagram of the distribution line. Consider the power distribution lines, as shown in Fig. 1 where r and x are resistance and reactance of the line, V1 and θ1 are the supply side voltage and phase angle, V2 and θ2 are the outlet side voltage and phase angle, P and Q are the active and reactive power of the line, respectively. Phase relationship of the voltage of the supply side and the outlet side voltage are represented as follows: •
V1 = V1 e jθ 1 •
V 2 = V 2 e jθ 2
2.2 Convergence operation of branch point voltage In wiring lines with some branches as shown in Fig. 2, value of bifurcated node voltage is essential because conversion factors to power (αbb’, αcc’, αcd’) must be calculated based on the voltage values of both ends in a single line. That’s why the voltage information on the nodes b and c are needed. But, measuring these voltages is difficult because these nodes are located behind the wall. Thus, the bifurcated node point voltage behind the wall is estimated by a convergence calculations. First, assume that the node voltage Vb is defined as in the following equation by considering the percentage of resistance of the lines.
(1) (2)
Then, active power P and reactive power Q are expressed by the following forms. That was because the resistance component is relatively larger compared with the reactive component in the wiring line.
V2 (V1 − V2 ) r V V (θ − θ 2 ) Q≅ 1 2 1 r P≅
(3) (4)
Vb 0 =
In equation (3), the active power can be estimated only by voltage values of two points if the resistance value of the line is known. Since the voltage is almost constant the active power P is almost proportional to the voltage difference, while the reactive power Q has little effect on the voltage difference. Therefore, power flow analysis of active power can be carried out by measuring the voltage difference of the line. So, by replacing 1/r with α/Vs, equation (3) can be rewritten as the following equation.
⎛V P = ⎜⎜ 2 ⎝ Vs
⎞ ⎟⎟α 12 (V1 − V2 ) ⎠
r1' (Va − Vb' ) + Vb' r1 + r1'
(6)
Here, by using the voltage in (6) active power flowing into the two terminals Pd and Pc are defined as the following equations in a same manner with the percentage of each resistance value and the conversion factors to power.
⎛V' ⎞ ⎧ ⎫ r' Pd 0 = ⎜⎜ d ⎟⎟α cd ⎨Vc' + 2 ' (Vb 0 − Vc' ) − Vd' ⎬ r2 + r2 ⎭ ⎝ Vds ⎠ ⎩ ⎛V' ⎞ r2' Pc 0 = ⎜⎜ c ⎟⎟α cc ' r2 + r2' ⎝ Vcs ⎠
⎛ rP ⎜⎜Vb 0 − Vc' − 2 d' 0 Vd ⎝
⎞ ⎟⎟ ⎠
(7)
(8)
(5) These values are approximately estimated and not accurate because a voltage drop is caused by each load. Then, the total amount of voltage drops arising in r1 by Pd and Pc are computed by using the calculated values of active power Pd and Pc in (7) and (8). Thus, Vb is updated. After that, Vc, Pd, Pc, Pb are calculated again in a same way. Then the above calculation steps are repeated until all values converge into
Here, α12 is defined as the rate of change in voltage difference against the changes in the load power consumption when a known load (we call this as a reference load) is connected to the outlet and α12 is referred to as a conversion factor to power. In other words, it is the
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fixed ones. As a result, the active power in all branches is estimated without knowing the bifurcated point voltage. [5]
(a) Measurement results of current Fig. 2. Indoor line model. 2.3 Estimation method for energy consumption by wiring connections To estimate power with the proposed method, it is necessary to know the wiring connections. The connections, however, can’t be easily checked because they are placed behind the wall. So, the method that estimates line wiring connections from the outlet voltage is proposed. Distribution line is considered as the model shown in Fig. 3. Firstly, current flows to the point d’ when load is connected at d’ point. Thus, voltage drop rises by line resistance of the distribution line. At that time, outlet voltage changes because of the effect of the voltage drop of b’ point between a-b and c’ point between a-c. Therefore, the line wiring connections can be estimated by comparing the amount of change in the voltage for each outlet with load. Electrical equipment that don’t use outlets such as lighting and equipments that are connected by special lines such as air conditioners can’t be applied in the proposed method. So, usage of such equipments is monitored by measuring the current. Fig. 4 shows the measurement results of current and power when the number of lighting units was changed. From Fig. 4, the waveforms of current and power look like same. Thus, by using current graph, usage of the lighting can be estimated. Therefore, by combining this method and the proposed method that estimates power by outlet voltage, the detail analysis will be possible. As a result, effective energy saving and management can be expected. [5]
(b) Measurement results of power Fig. 4. Measurements for the lighting units.
3. Estimation Method for Line Condition of a Building with Electrical Equipments connected 3.1 Estimation method for line condition when electrical equipments are connected The line condition where the electrical equipments are connected was estimated at one of the rooms of Kyushu Institute of Technology. Since then, all experiments were carried out in that room. The layout of the outlets and the distribution board in the room is shown in Fig. 5. Line condition estimation method was applied by allocating voltmeters at all outlets and at the distribution boards as shown in Fig. 5. The load to determine the condition factor is an 800W halogen heater. Load to determine factor was connected in outlet 1, after that, by handing no load condition of 30s and load condition of 60s for five times, the changes in the voltage were measured to estimate the line condition when load is connected. After that, the previous operation has been performed in order to outlet 2, outlet 3, and outlet 4. As a result, voltage waveform became as shown in Fig. 6. In this case, the ceiling outlets are different system. Therefore, Line condition was estimated as shown in Fig. 7 by measuring the voltage changes when a load determining factor connection was switched on-off at each outlet.
Fig. 3. Simplified circuit diagram of the distribution line. 325
Simple Measurement System for Indoor Power flow Distributions using Voltmeters at Electrical Outlet
Line model to be estimated is shown in Fig. 8. Fig. 9 shows the experimental results that compare the estimated power and the measured power with power meter at outlet 4. An overview at the estimated power waveform and the measured power waveform is showing that the result is almost the same as illustrated in Fig. 9. Power estimated by this estimation method, however, lacks of accuracy because the power consumption doesn’t match. Estimated power is the power consumption of all equipment which is connected to the outlet. On the other hand, measured power is considered as the power consumption of the load to determine the factor. So, Fig. 10 compares the waveforms of the measured power by power meter to the estimated power. Estimated and measured values are almost the same from this result. Thus, line condition can be estimated even if the electrical equipment is connected to the outlet.
Fig. 5. Output placement of measurement room.
Fig. 8. Simplified line model for the line condition estimation.
Fig. 6. Voltage waveform of the electric outlets and the distribution boards with a load sequenced at every outlet.
Fig. 9. Estimated waveform and measured waveform of outlet 4 in the line to be estimated.
Fig. 7. Line condition of measurement room.
Fig. 10. Comparison between estimated power and measured power.
3.2 Method validation in a real distribution system
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(a) Outlet 1 power consumption
(b) Outlet 2 power consumption
(c) Outlet 3 power consumption
(d) Outlet 4 power consumption
(d) Outlet 5 power consumption Fig. 11. Power consumption at each outlet. 327
Simple Measurement System for Indoor Power flow Distributions using Voltmeters at Electrical Outlet
measurement method on a line where some equipments are connected. Equipment which is connected in each outlet is discerned by this analysis. As a result, This method has advantages such as avoidance of overload connection. In addition, forgetting-to-turn-off is discriminated by combining this analysis result to current information. Therefore, specific energy conservation provision can be expected by advertising this result to user of electrical equipments on a regular basis.
4. Application of Simple Measurement System for Indoor Power Flow in Actual Distribution 4.1 Power usage analysis results in actual distribution system Simple measurement system for the indoor power flow was applied at five outlets at the measurement room. In that room, power usage for five days was analyzed. Electrical equipments are connected at each outlet and the results are shown in Table 1 and Fig. 11. Outlet 1 seems to be using the printer from time to time. But, outlet 1and outlet 4 were turned on during the day because the Personal Computer (PC) has been collecting data at 30 minute intervals and 1 minute interval. Therefore, Power consumption nearly equals a constant value. The term, forgetting-to-turn-off, is defined as the condition when the power consumption continues in a time zone where lighting was turned off. Then, outlet 2 was low possibility for forgetting-to-turn-off because it doesn’t consume too much power. Variation of power consumption of outlet 3 and ceiling outlet was active because the numbers of PCs were large. In addition, power consumption was not 0 in off time zone. This is because PCs were at standby conditions and the displays consumed power. With this method, transition of power in each outlet can be visualized. Thus, these results can leverage preventing overload connection by verifying power consumption of each outlet when equipment which has largest power consumption was used. In addition, to examine forgetting-to -turn-off equipment is possible by watching the lighting and power consumption at the same time Therefore, effective energy conservation measures can be expected.
References [1] Douglas J. Arent, Alison Wise and Rachel Gelman, The status and prospects of renewable energy for combating global warming: Energy Economics 33, 2011, p.584593. [2] Ali Keyhani, “Design of Smart Power Grid Renewable energy Systems”, Wiley, 2011 [3] Yaser S. Qudaih and Takashi Hiyama, “Utilization of Energy Capacitor Systems in Power Distribution Networks with Renewable Energy Sources”, JEMAA International journal 4, 2010, p.2 [4] Ersan Kabalci, Yasin Kabalci and Ibrahim Develi, “Modeling and analysis of a power line communication system with QPSK modem for renewable smart grids”, Electrical Power and Energy Systems 34, 2012, pp.19– 28 [5] G.Nakano and Y.Mitani (Kyushu Institute of Technology), “Power Distribution Monitoring for Each Power Outlet by Simple Measurements”, IEEJ. Power Engineering and Power System Engineering, 2012 Yuhei Nozaki received the B.Sc. degree in Electrical Engineering and Electronics from Kyushu Institute of Technology, Japan, in 2012. Currently, he is a student of Master’s course at Department of Electrical Engineering and Electronics in Kyushu Institute of Technology, Japan. His research interests are monitoring and analysis of power system.
Table 1. Equipments connected at each outlet Outlet 1 Outlet 2 Outlet 3 Outlet 4 Outlet 5
PC, printer, electric pod PC (two desktop, two display) PC (five desktop, six display) PC, UPS PC (five desktop, four display)
5. Conclusion
Yasunori Mitani received his B.Sc., M.Sc. and D.Eng. degrees in Electrical Engineering from Osaka University, Japan in 1981, 1983 and 1986, respectively. He is currently a professor at the Department of Electrical Engineering and Electronics, Kyushu Institute of
Power consumption was analyzed by measuring the voltage of the electrical distribution board and the electrical outlets in multi-point simultaneously. In addition, method which can estimate power consumption even if the equipments are connected to the outlet was proposed. Power usage of each outlet was analyzed by applying this
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Technology (KIT), Japan. At present he is the Head of Green Innovation Education and Research Center of KIT. His research interests are in the areas of analysis and control of power system. He is a member of the Institute of Electrical Engineering of Japan and IEEE.
Qudaih Yaser graduated from the University of Engineering and Technology, Lahore, Pakistan in 1996 as an electrical engineer. He completed his M.Sc. and Ph.D. from Kumamoto University, Japan in Electrical Engineering. He is currently am assistant professor at the Department of Electrical Engineering and Electronics, Kyushu Institute of Technology, Japan. His area of interest including power system is renewable energy and smart grid applications.
Masayuki Watanabe received the B.Sc., M.Sc., and D.Eng. degrees in Electrical Engineering from Osaka University, Osaka, Japan, in 2001, 2002 and 2004, respectively. Currently, he is an Associate professor at Dept. of Electrical and Electronic Engineering of Kyushu Institute of Technology, Japan. His research interests are in the area of analysis of power system.
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